2.7 Data analysis
To develop a general pattern of ecosystem services in relation to plateau pika disturbance across the five sites, two-way analysis of variance (ANOVA) with a general linear model (GLM) was used to analyze the effects of plateau pika disturbance, the sites and their interactions on palatable plant biomass, plant species richness, soil water storage, soil organic carbon, soil total nitrogen, soil total phosphorus and soil total potassium stocks. In the model, the abovementioned parameters acted as response variables, and plateau pika disturbance, site and their interactions were introduced as fixed effects.
In addition, the paired-samples T test was used to examine the differences in palatable plant biomass, plant species richness, soil water storage, soil organic carbon stock, soil total nitrogen stock, soil total phosphorus stock and soil total potassium stock between the disturbed and undisturbed plots at each site. Here, the “disturbed plots” and “undisturbed plots” were regarded as one-to-one corresponding samples, the paired plots were considered random factors, and the disturbed/undisturbed plots were considered to be fixed effects, which were used to verify the results from five sites and to support the general pattern.
To clarify the responses of palatable plant biomass, plant species richness, soil water storage, soil organic carbon stock, soil total nitrogen stock, soil total phosphorus stock and soil total potassium stock to the plateau pikas disturbance intensity, a linear model (LM) was used to examine the relationships between palatable plant biomass, plant species richness, soil water storage, soil organic carbon stock, soil total nitrogen stock, soil total phosphorus stock and soil total potassium stock and active burrow entrance densities in all disturbed plots and in an individual site. The active burrow entrance densities were considered to be a fixed factor, and they were used to construct regression curves between palatable plant biomass, plant species richness, soil water storage, soil organic carbon stock, soil total nitrogen stock, soil total phosphorus stock and soil total potassium stock and active burrow entrance densities.
Significant differences were assessed at P <0.05. All statistical analyses were performed with the SPSS 17.0 software package from SPSS Inc., Chicago, IL, USA.